This study examines the effect of sleeping position on the cardiorespiratory status, growth, sleep and behavior of the healthy preterm (< 36 weeks gestational age) and term infant. We evaluate infants thermoregulatory capabilities when presented with warming conditions. Healthy preterm and term infants (n=18) are studied during daytime naps to evaluate their Evaporative Water Loss rates. Preliminary data show differences in apnea, bradycardia, and oxygen desaturations based on body position, especially with regard to feedings. The effect of body position on sleep architecture is also being studied.